A happy nihilist? Sounds like a contradiction. But for one thing, you are free from the burden of man-made rules and myths about the so-called meaning of life. Imagine the burden of expectation you would have placed on you to do things a certain way, or to follow your so-called destiny... You are free from those restraints. No false hopes leading to devastating dissapointments.
"It's only after we have lost everything, that we are free to do anything." -Tyler Durdon. Fight Club is one of the BEST movies of all time depicting a Nihilist of sorts.
Your life doesn't lack meaning, because that "meaning" never existed in the first place. There must be a comfort of sorts in being perfectly rational about your existence, and you are on your way to becoming your true self.

Your life is yours to create. A blank canvas free from rules, religion and everything else.
Nihilism doesn't have to be overly pessimistic and passive. It can be active, which is probably the way Nietzsche envisioned the concept.

Anyway, that's my thought. I hope that helps.

Btw, I'm not a nihilist, at least I don't think I am.
I'm just me.